Most modern electronic devices, e.g., computers and cellular telephones, may include semiconductor devices. Semiconductor devices may be manufactured as discrete devices, e.g., transistors, and/or as integrated circuits that may include many interconnected devices on a single semiconductor substrate. The behavior of semiconductor devices may be manipulated by the controlled addition of impurities, e.g., dopants. Design considerations may include device speed and power consumption when designing semiconductor devices and the electronic devices that may include them.
For example, Silicon (“Si”) may be used as a substrate and Germanium (“Ge”) may be used for an active channel layer. The unequal lattice constants of Si and Ge may require the inclusion of a transition or buffer layer or layers between the Si substrate and the Ge active channel layer. Without these buffer layers, lattice mismatch may result in defects that may make a device inoperable or may cause a device to fail prematurely. In order to address lattice mismatch, a combination of Si and Ge, e.g., Si1−xGex (x=0.4-0.7), may be used for these buffer layers. Although these buffer layers may address the lattice mismatch, they may not provide a complete solution. A Ge active channel layer may suffer from parallel conduction between the active channel and the Si1−xGex buffer layers because of Si1−xGex's relatively low band gap. As a result of parallel conduction between the active channel and the Si1-xGex buffer layer, a relatively large gate voltage may be needed to shut off a device. The Si1−xGex—Ge interface may also provide a relatively low valence band offset that may result in inadequate carrier confinement and an associated decrease in carrier mobility. As a result, a semiconductor device constructed with a Si substrate, Ge active channel layer and Si1−xGex buffer layers, may be slower and may consume more power than a semiconductor device without these limitations.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art.